When doctors treated the man for the first time, he had already been suffering from severe gut pain, fever and was vomiting for a week.

Blood tests showed the area below his ribs was tender, and he had an increased number of white blood cells, which typically indicate the body is fighting an infection. The condition came out to be signs of Anisakiasis, which when further investigated revealed that the man had consumed sushi. After ingesting the contaminated food, the worms can get into the wall of the stomach or intestines which can cause intense gastrointestinal pain, vomiting, and nausea.

This infection can be contracted by eating raw and undercooked fish.

A special kind of net was used to remove the larvae "and the patient's symptoms resolved immediately", the team from a central Lisbon hospital said.

The authors said that most of the cases reported to date were from Japan, where a raw fish diet is very common.

"Owing to changes in food habits, anisakiasis is a growing disease in Western countries, which should be suspected in patients with a history of ingestion of raw or uncooked fish", Dr Carmo explained.

Researchers also learned that people who eat a lot of sushi are at risk of exposing themselves to risky levels of mercury, which can lead to heart disease, decreased cognitive performance and other issues with brain and nervous system development.

"However, it has been increasingly recognised in Western countries", the doctors wrote.

"Patients can have allergic symptoms". But before it dies, it produces an inflamed mass in the esophagus, stomach or intestine. According to them, sushi may pose a serious health hazard as it has parasites present in undercooked fish and seafood.

However, according to another study made in Spain, about 56 percent of blue whiting fish had the worm that causes anisakiasis.

Dr. Donald Hensrud, medical director of the Mayo Clinic Healthy Living Program and specialist in nutrition and preventive medicine, told CBS News that pregnant women and people with compromised immune systems, such as HIV patients or individuals taking biologic drugs, should avoid raw or undercooked fish and seafood. "They're not cooking the fish so that is the only prevention method, keeping it cold", he said. If not, people should store it at -4 degrees Fahrenheit for three days to kill parasites.